What hostile creatures intercept the heroes in Splatoon Raiders?

The hostile creatures that intercept the heroes in Splatoon Raiders are Salmonids.

Salmonids are fish-like enemies already established in the Splatoon universe, especially through the Salmon Run cooperative mode in Splatoon 2 and Splatoon 3. In Raiders, they occupy the Spirhalite Islands and attack the Mechanic and Deep Cut as they search for treasure and salvage.

The enemies are more than a generic group of aquatic monsters. Raiders features ordinary Salmonids as well as stronger varieties and boss encounters, giving combat a progression system tied to exploration. Defeating them provides materials and opportunities to improve weapons, gadgets, and other equipment.

A frequent mix-up is confusing Salmonids with Octarians. Octarians are enemies associated with the Octarian army and its military campaigns, whereas Salmonids are the fish-like inhabitants encountered in Salmon Run and on the Spirhalite Islands. Inklings, meanwhile, are generally allies or playable characters rather than the hostile group in this question.